sqlite - Flutter FutureBuilder未使用sqlite的数据进行构建

Question

我是个新手，正在尝试编写可从sqlite获取值(value)的应用程序。根据我的尝试，它需要使用FutureBuilder小部件。

但是我写的以下代码，FutureBuilder小部件似乎是从sqlite获取数据的，但是从未调用过“builder”属性:

import 'package:flutter/material.dart';
import 'package:flutter_spinkit/flutter_spinkit.dart';
import 'package:flutterapp/dbHelper.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      routes:{
        "/": (context) =>Test()
      }
    );
  }
}

class Test extends StatefulWidget {
  @override
  _TestState createState() => _TestState();
}

class _TestState extends State<Test> {

  bool nameCheck = false; // Use to check name textfield has correctly be inputed
  TextEditingController nameController = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body:Column(
          children: <Widget>[
            SizedBox(height:300),
            Row(
              children: <Widget>[
                Expanded(
                    child: TextField(
                      controller: nameController,
                    )
                ),
                IconButton(
                  icon: Icon(Icons.check_circle),
                    onPressed:(){
                      return FutureBuilder(
                          future: getData(nameController.text),
                          builder: (BuildContext context, AsyncSnapshot<List<Map>>snapshot) {
                            print("Start future"); // never get printed
                            List<Widget> children;
                            if (snapshot.hasData) {
                              children = <Widget>[
                                Builder(
                                    builder: (BuildContext context) {
                                      print("got data");
                                      final result = snapshot.data;
                                      print(result) ; // never get printed
                                      setState(() {
                                        nameCheck = true;
                                      });
                                      return Container();
                                    })
                              ];
                            } else {
                              children = <Widget>[
                                AlertDialog(
                                    content: SpinKitCircle(
                                      color: Colors.white,
                                      size: 80.0,
                                    ))
                              ];
                            }
                            return Center(
                                child: Container(
                                    color: Colors.blue,
                                    child: Column(
                                      mainAxisAlignment:
                                      MainAxisAlignment
                                          .center,
                                      crossAxisAlignment:
                                      CrossAxisAlignment
                                          .center,
                                      children: children,
                                    )));
                          });}
                )
              ],
            ),
            Builder(
              builder: (BuildContext context){
                if (nameCheck == true){
                  return Text("test");
                }
                return Container();
              }
            )
          ],
        )
    );
  }
}

Future<List<Map>> getData(String input_name) async{
  final dbHelper = DBHelper.instance;
  await dbHelper.database;
  final result = await dbHelper.query("SELECT * FROM Guest WHERE Name = \"$input_name\"");
  print(result); // This get printed
  return result;
}

DBHelper代码如下，基本上它只是建立一个sqlite数据库和一些数据库操作:

import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';
import 'dart:io';
import 'package:path_provider/path_provider.dart';

class DBHelper {
  static final _databaseName = "MonetaryDB.db";
  static final _databaseVersion = 1;

  static final create_table_Test = "CREATE TABLE \"Guest\" (\"Name\"    TEXT NOT NULL PRIMARY KEY, \"Money\" INTEGER, \"Person\" INTEGER)";

  static final String insert_guest = "INSERT INTO Guest (Name, Money, Person) VALUES (\"testname\", 1000, 1)";

  DBHelper._privateConstructor();

  static final DBHelper instance = DBHelper._privateConstructor();

  static Database _database;
  Future<Database> get database async {
    if (_database != null) {
      return _database;}
    else{
      _database = await _initDatabase();
    return _database;}
  }

  _initDatabase() async {
    Directory documentsDirectory = await getApplicationDocumentsDirectory();
    String path = join(documentsDirectory.path, _databaseName);
    return await openDatabase(path,
      version: _databaseVersion,
      onCreate: _onCreate,
    );
  }

  Future _onCreate(Database db, int version) async {
    await db.execute(create_table_Test);
    await db.rawInsert(insert_guest);
  }

  Future<int> insert(String statement) async {
    Database db = await instance.database;
    return await db.rawInsert(statement);
  }

  Future<List<Map>> query(String statement) async {
    Database db = await instance.database;
    return await db.rawQuery(statement);
  }

  Future<int> update(String statement) async{
    Database db = await instance.database;
    return await db.rawUpdate(statement);
  }

  Future<int> delete(String statement) async{
    Database db = await instance.database;
    return db.rawDelete(statement);
  }
}

如果仅将IconButton onPressed函数更改为 setState((){nameCheck = true})，将显示 Text("test")小部件，因此问题一定是FutureBuilder。另外，getData()函数可以从sqlite数据库获取正确的结果

我不知道为什么FutureBuilder无法构建，有人对此有任何想法吗？
谢谢!

Answer 1

因此，在注释部分的帮助下，我更改了代码，它可以正常工作:

...
  Widget build(BuildContext context) {
    return Scaffold(
        body:Column(
          children: <Widget>[
            SizedBox(height:300),
            Row(
              children: <Widget>[
                Expanded(
                    child: TextField(
                      controller: nameController,
                    )
                ),
                IconButton(
                  icon: Icon(Icons.check_circle),
                    onPressed:(){
                    return showDialog(
                      context: context,
                      builder: (BuildContext context){
                        return AlertDialog(
                          actions: <Widget>[
                            SizedBox(
                              width: 300,
                              height: 300,
                              child: FutureBuilder(
                                  future: getData(nameController.text),
                                  builder: (BuildContext context, AsyncSnapshot<List<Map>>snapshot) {
                                    if (snapshot.hasData) {
                                      final result = snapshot.data;
                                      SchedulerBinding.instance.addPostFrameCallback((_) => setState(() {
                                        nameCheck = true;
                                      }));
                                      Navigator.pop(context, true);
                                    }
                                    else {
                                      return Container(
                                          child: SpinKitCircle(
                                            color: Colors.white,
                                            size: 80.0,
                                          ));
                                    }
                                    return Container(color: Colors.blue);
                                  })
                            ),
                          ],
                        );
                      }
                    );
                  }
                )
              ],
            ),
            Builder(
              builder: (BuildContext context){
                if (nameCheck == true){
                  return Text("test");
                }
                return Container();
              }
            )
          ],
        )
    );
  }
...

其他代码仍然相同。

就像上面的评论部分所建议的那样，主要问题是将没有地方要为FutureBuilder构建小部件。为了解决此问题，我将FutureBuilder小部件放入AlertDialog小部件中，因为在加载时我仍然希望保留SpinKitCircle小部件。

我还放弃了FutureBuilder小部件末尾的Column小部件，并删除了FutureBuilder小部件开头的Builder小部件，当没有Column时不再需要。

上面的代码仍然引发可接受的异常:“在构建期间调用setState()或markNeedsBuild()”。但是整个过程仍然可以运行，因此我将在第二天尝试修复该问题。

感谢您在评论部分的建议。